IMPROVED MICROSURGICAL ANASTOMOTIC PATENCY WITH LOW-MOLECULAR-WEIGHT HEPARIN

Blood flow to a free flap may be impaired by thrombotic occlusion at t he anastomosis or by microemboli occluding microvessels. The purpose o f this study was to test the hypothesis that unfractionated heparin (U FH) or low molecular weight fractions of heparin (LMWH) could improve both the patency of microvascular anastomoses and microcirculatory per fusion. Sixty-six rats underwent orthotopic elevation of 3- x 10-cm ep igastric free flaps. Animals received a single injection of either veh icle, UFH or LMWH, prior to microvascular clamp application and pedicl e division. Anastomotic patency and tissue survival area were assessed on postoperative day 7. Anastomotic patency was significantly improve d in both the UFH and LMWH groups. Total tissue survival area in those flaps with anastomotic patency was significantly improved in the UFH and the LMWH groups. Although both UFH and LMWH significantly elevated activated partial thromboplastin times (APTT) and anti activated clot ting factor X (anti-Xa) activity over controls, UFH had its greatest e ffect on APTT, and LMWH on anti-factor Xa activity. Hematomas develope d only in the UFH group. Thus, although both UFH and LMWH improved mic rocirculatory perfusion, as indicated by increased flap survival, only LMWH improved anastomotic patency while minimizing hemorrhage.